Azo dyes and related compounds are prevalent environmental contaminants and pose a significant risk to human health. With a current inventory of more than 40,000 dyes, estimates suggest greater than 15% of the current production [at least 128 tons per day] are released into the environment through industrial discharges and from waste sites where manufacturing by-products have been disposed. The major significance to human health of these dyes is in the carcinogenic potential of the aromatic amines, entering the environment either as by-products of manufacturing or as immediate metabolic products from the reductive cleavage of the azo linkage. Clinical and epidemiological studies have established links of human exposure to dyes and dyestuffs and to the use of dyes in the textile industry with the development of cancer. The research program proposed in this project utilizes a physicochemical model to determine significant factors which relate recalcitrance to the degradation, persistence and fate of azo dyes, related dyestuffs and their degradation or biotransformation products in the environment. The central question is: Why are hazardous wastes recalcitrant to most treatment processes and persist in the environment, but, yet given certain conditions, they are transformed to more toxic substances which can become more mobile environmentally and present a greater threat to human health? Two objectives are proposed for this research, with specific aims central to the laboratory and providing opportunities for collaborative research with colleagues in other projects of this application. OBJECTIVE 1 is a chemical and biochemical approach to examine and evaluate the abiotic bases for the recalcitrance of various azo dyes and structurally related chemical moieties, such as aromatic amines and aromatic sulfonic acids, to understand the processes that influence their environmental persistence or their degradation, biotransformation and/or mineralization. OBJECTIVE 2 is an experimental and theoretical physical chemical approach to examine and evaluate extrinsic and intrinsic factors that are determinants in the recalcitrance of the dyes and related compounds by an investigation of physicochemical and theoretical chemical parameters that lead to their environmental persistence and fate. The following specific aims will be addressed: Aim 1 - to investigate the determinants of the abiotic stability of azo dyes and structurally related chemical moeities of the azo dyes [in collaboration with Caruso, Aim 2 - to investigate the determinants of the biotic stability of azo dyes and structurally related chemical moeities of the dyes [in collaboration with Loper and Bishop]; Aim 3 - to investigate both intrinsic and extrinsic factors that impact the biological and chemical processes determining the persistence and fate of azo dyes and related compounds.